Surface Grafting of Poly(l-glutamates). 2. Helix Orientation

Abstract

In this paper the average helix orientation of surface-grafted poly(γ-benzyl L-glutamate) (PBLG), poly-(γ-methyl L-glutamate) (PMLG), and poly(γ-methyl L-glutamate)-co-(γ-n-stearyl L-glutamate) (PMLGSLG 70/30) was investigated by means of FT-IR transmission spectroscopy. The theoretical relation between the average tilt angle (θ) and the absorption peak areas of three different backbone amide bands could be calculated because their transition dipole moment directions with respect to the helix axis were known. From the normalized absorptions, the average tilt angles of grafted helices of PBLG, PMLG, and PMLGSLG 70/30 were determined. The somewhat larger average angle of PMLG helices of 35 ( 5°with respect to the substrate compared to the value of 32 ( 5°of PBLG was due to the higher grafting density of PMLG. Because of the smaller helix diameter as a result of the smaller size of the methyl side group, more PMLG helices grew on the same surface area. Sterical hindrance and unfavorable polar interactions between unidirectional aligned helices forced the PMLG helices in a more upright arrangement. The even more perpendicular orientation of PMLGSLG 70/30 (48 ( 6°) could be the result of incorporation of mainly γ-methyl L-glutamate N-carboxyanhydride (MLG-NCA) monomers during the initiation step. Incorporation of the much larger γ-n-stearyl L-glutamate N-carboxyanhydride (SLG-NCA) monomers afterward lead to enlarged angles with respect to the substrate. Due to swelling, a pronounced change in helix orientation of grafted PMLGSLG 70/30 in n-hexadecane was observed, resulting in an almost perpendicular helix orientation.

Sum-frequency spectroscopy and imaging of aligned helical polypeptides

“…Table I summarizes the average angle and for the five points. The average value of the tilt angle is which compares well with the IR tilt angle measurements of PBLG films measured by Wieringa et al [43]. The orientation distribution of the PBLG molecules on the sample was imaged using sum-frequency from the N-H band in the following manner.…”

“…The spectral features below 1300 cm are caused by overtones, bends, and scissors of various molecules. The IR vibrational signatures are consistent with [43]. Fig.…”

Poly(γ-benzyl-l-glutamate) Peptides Confined to Nanoporous Alumina: Pore Diameter Dependence of Self-Assembly and Segmental Dynamics

“…27 In particular, the polypeptide poly(γ-benzyl-L-glutamate) (PBLG) has been studied as a model rigid-rod polymer in solution, 30 in the melt, [26][27][28]31 and grafted to surfaces. 32 Here we report the strong dependence of the segmental dynamics of PBLG synthesized in self-ordered AAO with mean D values of 25,35,65,200, and 400 nm and a pore depth of 80-95 µm on the pore diameter. Whereas both released PBLG nanorods (by etching the AAO) of all diameters and nanorods located in AAO with D values of 200 and 400 nm show bulklike behavior, considerably different segmental dynamics was found for PBLG confined to AAO hard templates with D values equal to or smaller than 65 nm.…”

Polypeptoid Brushes by Surface-Initiated Polymerization of N-Substituted Glycine N-Carboxyanhydrides

“…35,43-45 They attributed the layer thickness limitation to the formation of chemically or physically “dead” chain ends, which is commonly regarded as major limitation on controlling NCA polymerization, also in solution. 29 However, the mechanisms responsible for chemical inactivation of NCAs should not apply for NNCAs as these cannot deprotonate at the nitrogen atom, the attack at the 2-position of the ring leading to hydantoic acids termini is blocked 46 , and the β-sheet or α-helix formation within the brush 34 can be ruled out due to the lack of inter- or intramolecular hydrogen bonding.…”